Advances in manufacturing procedures in modern technology have depended in many instances on the purification of substances used as both reagents and as materials, in the presence of which various processes are conducted. The purification of many such substances, typically liquids and gases, has required the removal of impurities which are either heterogeneous (such as particles and macromolecules) or homogeneous (such as dissolved substances). In many instances both types of impurities may be present. Typically, heterogeneous impurities are removed by filtration techniques and devices in which the particles are physically retained by some sort or perforate or porous medium. Other methods and purification techniques are typically chosen to remove homogeneous impurities. Many of these techniques involve chemical modification of the homogeneous impurity and/or the affinity and attraction of the homogeneous impurity to a material which removes the homogeneous impurity from the fluid.
In many areas of modern technology, the concentration of impurities above several parts per million (ppm) cannot be tolerated. Indeed, in certain technologies, such as in the manufacture of semiconductor devices, the concentration of impurities in both the substances used as reagents as well as other materials, in the presence of which the processes are conducted, can still be detrimental even at levels at or below several parts per billion (ppb). For example, in many of the process gases employed in manufacturing semiconductor devices, even minute amounts of impurities, such as oxygen, moisture, carbon dioxide, and organic compounds such as methane, can be absorbed on the semiconductor wafer, causing degradation of performance, reduced manufacturing yield and adverse reliability.
A variety of devices and methods have been suggested for high level purification of fluids, including the use of a reactive membrane. Reactive membranes are disclosed, for example, in U.S. Pat. Nos. 5,196,380, 5,637,544, and 5,829,139. These patents, as well as any other patents, patent applications, and publications referenced in this application, are incorporated by reference. While a reactive membrane may be capable of purifying fluids such as gases used in the manufacture of semiconductors to a very high level, the capacity of the reactive membrane with respect to the space occupied by the membrane may be insufficient to keep the process online for the desired time before shutdown for regeneration or replacement of the reactive membrane. For example, a reactive membrane may be capable of reducing a contaminant such as oxygen in a gas stream to an acceptable level, e.g., a few parts per billion (ppb) or even to trace amounts, i.e., 1 ppb or less. However, the capacity of the reactive membrane is low, e.g., only about 1 or 2 liters of oxygen (at standard conditions) removed per liter of reactive membrane, and breakthrough of oxygen at unacceptable levels will occur relatively quickly, necessitating shutdown of the gas stream and replacement or regeneration of the reactive membrane. Increasing the capacity of the reactive membrane by adding one or more additional membrane layers will result in an undesirable increase in the pressure drop through the reactive membrane. Alternatively, increasing the capacity of the reactive membrane by increasing the nominal upstream surface area of a single layer reactive membrane, e.g., from 0.75 in2 to 1.5 in2, will require a larger membrane housing, which may be equally undesirable.